Systems, methods, and devices for capacitive sensing with sinusoidal demodulation

ABSTRACT

Systems, methods, and devices improve the sensitivity of capacitive sensors. Devices may include an attenuator configured to receive an input from at least one sense electrode of a capacitive sensing device. The attenuator may be included in a sensing channel of a capacitive sensor. Devices may further include a signal generator coupled to an input of the attenuator. The signal generator may include one or more processors configured to generate a sinusoidal signal based, at least in part, on one or more noise characteristics of a scan sequence associated with one or more transmit electrodes of the capacitive sensing device, and provide the sinusoidal signal to the input of the attenuator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.Provisional Patent Application No. 63/006,298 filed on Apr. 7, 2020,which is incorporated herein by reference in its entirety for allpurposes

TECHNICAL FIELD

This disclosure generally relates to capacitive sensors, and morespecifically, to improving the external noise immunity of suchcapacitive sensors.

BACKGROUND

Devices and systems, such as mobile communications devices, may includevarious input devices such as touchscreens and buttons. The touchscreensand buttons may utilize one or more sensing modalities to receive theinputs from an entity, such as a user of a mobile communications device.An example of such a modality may be capacitive sensing in which atouchscreen or button may include conductive elements which may be usedto obtain various capacitance measurements. For example, a touchscreenmay include an array of electrodes and a touchscreen controller may beused to measure capacitances associated with those electrodes. However,many capacitive sensors remain limited because they are prone to besensitive to the external noise, as may result from their sensingchannels are sensitive to the harmonics of the operation frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an example of a device for noise immunityenhancement of capacitive sensors, configured in accordance with someembodiments.

FIG. 1B illustrates another example of a device for noise immunityenhancement of capacitive sensors, configured in accordance with someembodiments.

FIG. 2 illustrates an example of an improved charge-to-time converter,configured according to some embodiments.

FIG. 3A illustrates an example of a variable gain attenuator, configuredin accordance with some embodiments.

FIG. 3B illustrates another example of a variable gain attenuator,configured in accordance with some embodiments.

FIG. 3C illustrates yet another example of a variable gain attenuator,configured in accordance with some embodiments.

FIG. 4 illustrates another example of the improved charge-to-timeconverter, configured according to some embodiments.

FIG. 5A illustrates an implementation of an example of a variable gainattenuator, configured in accordance with some embodiments.

FIG. 5B illustrates an implementation of an example of an attenuator,configured in accordance with some embodiments.

FIG. 6 illustrates an example of a variable gain attenuator, configuredin accordance with some embodiments.

FIG. 7 illustrates an example of a system for noise immunity enhancementof capacitive sensors, configured in accordance with some embodiments.

FIG. 8 illustrates a flow chart of an example of a method for scanningusing one sensing slot of capacitive sensors, implemented in accordancewith some embodiments.

FIG. 9 illustrates a flow chart of another example a method for scanninga panel or other sensor array using multiple scan slots, implemented inaccordance with some embodiments.

FIG. 10 illustrates a flow chart of an additional example of a methodfor enhancing sensitivity of capacitive sensors by providing a transmitsignal phase calibration, implemented in accordance with someembodiments.

FIGS. 11A and 11B illustrate diagrams of examples of an attenuator inputand output having different numbers of gain steps, implemented inaccordance with some embodiments.

FIGS. 12A and 12B illustrate diagrams of examples of signals sensed byone or more sensing channels, implemented in accordance with someembodiments.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the presented concepts. Thepresented concepts may be practiced without some or all of thesespecific details. In other instances, well known process operations havenot been described in detail so as not to unnecessarily obscure thedescribed concepts. While some concepts will be described in conjunctionwith the specific examples, it will be understood that these examplesare not intended to be limiting.

FIG. 1A illustrates an example of a device for noise immunityenhancement of capacitive sensors, configured in accordance with someembodiments. As will be discussed in greater detail below, a capacitivesensor may include various components configured to utilize capacitancemeasurements to identify the presence of objects. As disclosed herein, apresence may refer to a contact, hover, or other sensed event. Forexample, a capacitive sensor may utilize various electrodes to sense theproximity or contact with a user's finger based on capacitance-basedmeasurements. More specifically, the capacitive sensor may include asensing channel that has an input attenuator that is configured toreceive a sensed input from a sensing device, such as a touch panel thatmay include a capacitive touch screen. As will be discussed in greaterdetail below, a device, such as device 100, may be configured tomodulate an input signal received by the input attenuator to reducenoise and increase the sensitivity of downstream components used to makemeasurements when sensing operations are performed by the capacitivesensor.

Accordingly, device 100 includes input 102 which may be an input that iscoupled to one or more components of a sensing device. As similarlydiscussed above, capacitive sensors may include sensing devices thatinclude electrodes used to make various measurements that may be used toinfer the presence of an adjacent or contacting object, such as afinger, stylus, or other conductive object. It will be appreciated thatany suitable conductive object may be used. Moreover, such objects maybe made of any suitable materials that change the physical surroundingof sensing electrodes such that the capacitance changes. Morespecifically, a sensing device may be a touch panel that includes anarray of transmit electrodes as well as an array of receive electrodes.A scan sequence may be implemented in which a signal is sent through oneor more of the transmit electrodes, and measurements are made at one ormore of the receive electrodes. The measurements may be capacitancemeasurements, and may be affected by an adjacent or contacting object.For example, a user's finger contacting or hovering near the touch panelat a particular location may affect capacitance measurements ofelectrodes at that location. The sensed signal from the receiveelectrodes may be received at input 102.

Device 100 further includes attenuator 104 which is configured to set aninput impedance seen by a sensing device, such as the touch panel, andis also configured to set an output impedance seen by other componentsof sensing channel, as will be discussed in greater detail below withreference to at least FIGS. 3 and 4. Accordingly, the sensed signalreceived at input 102 may be coupled to an input of attenuator 104.Thus, according to various embodiments, attenuator 104 is configured toprovide several features. More specifically, it attenuates an inputsignal, it provides the feature of impedance conversion, it provides alow input impedance and a high output impedance, and it acts as acurrent source where the output current is determined based on the inputcurrent.

Device 100 additionally includes signal generator 106 which isconfigured to generate a signal that is configured to reduce particularcharacteristics of the input signal sensed at input 102. As will bediscussed in greater detail below, the sensed signal may be prone toexternal noise that may arise from various sources. For example, noisemay be generated by other components such as a liquid crystal display(LCD) panel, as well as capacitive coupling between components or even auser's finger, like charger noise. In various sensing channelembodiments, the noise may present as increased sensitivity at oddharmonics of a frequency that may be used during sensing operations. Forexample, a scanning sequence of electrodes included in touch panel mayinvolve a scanning burst implemented at a particular scanning frequency.The noise sources noted above and associated parasitic capacitances mayresult in increased sensitivity to the noise at odd harmonics of thescanning frequency. For example, increases in a measured signal mayoccur at a third, fifth, seventh, and ninth harmonic of the scanningfrequency. Such measured harmonics are not desirable as they are largelyproducts of noise characteristics of the sensing channel, and not theunderlying touch/hover that is being measured. Accordingly, somecapacitance sensing channels might be sensitive to odd harmonics of theoperation frequency.

Embodiments disclosed herein remove sensing channel sensitivity to theodd harmonics without major or expensive modifications of the channelitself. As will be discussed in greater detail below, this may beaccomplished by adding a mixer as part of the existing sensing channel.The mixer provides input current multiplication on non-negative numbersof harmonics (including zero, meaning the gain is equal to zero). Invarious embodiments, the mixer input waveform is a rectified sinusoidalsignal with a same frequency as a transmit signal. It will beappreciated that mixer implementations might be different in variousembodiments. For example, mixers might be implemented as variable gainamplifiers with discrete gain levels, or driven by a sigma-modulatoroutput. In one embodiment, the mixer is an on/off switch, that operatesat a relatively high over-sample frequency, e.g. 48 MHz for the 100 kHzof the transmit signal. As will also be discussed in greater detailbelow, various features of the mixer can be implemented inside of asensing channel by, for example, varying the attenuator gain at thefront of attenuator, as may be accomplished by using the previouslydescribed switch.

In various embodiments, the signal generated by signal generator 106 isconfigured to reduce or attenuate the effects of these noise sources onthe sensed signal. Signal generator 106 provides a rectified sinusoidalwaveform having a frequency determined by the operation frequency of atransmit signal. The waveform amplitude is configured to provide mixeroperation in a linear range and prevent analog saturation. In this way,adding an analog mixer, driven by the rectified sinusoidal signal at thefront of the sensing channel removes the sensitivity to the oddharmonics. In various embodiments, the operation frequency is configuredto provide a lowest noise level of output readings in the presence ofexternal noise (like LCD noise). Thus, the operation frequency isconfigured such that there is reduced overlapping in the frequencydomain of the noise spectrum with the sensing channel frequencyresponse. Removing sensitivity to the odd transmit frequency harmonicsprovides reduction in noise spectrums overlapping and additionallyprovides external noise attenuation. The result of noise attenuation isincreasing the signal-to-noise ratio of the capacitance sensing system.As discussed above, an output of signal generator 106 is coupled with amixer, such as mixer 108. Accordingly, mixer 108 is configured tomultiply the output of signal generator 106 with the sensed signalreceived at input 102, and provide the result as an input to attenuator104, as discussed above.

FIG. 1B illustrates another example of a device for the external noiseimmunity enhancement of capacitive sensors, configured in accordancewith some embodiments. As similarly discussed above, a device, such asdevice 110, may be configured to modulate an input signal received by aninput attenuator to reduce the off-band) noise (noise that is outside atransmit frequency) and increase the sensitivity of downstreamcomponents used to make measurements when sensing operations areperformed by a capacitive sensor.

As also discussed above, device 110 may also include input 102 andattenuator 104. In various embodiments, device additionally includesmodulator 112 which may be included in a signal generator and may becoupled to variable gain amplifier 114. Accordingly, as shown in FIG.1B, modulator 112 is configured to generate a signal that is configuredto reduce noise characteristics of the input signal sensed at input 102.Moreover, variable gain amplifier 114 is configured as a mixer, and isconfigured to combine the signal generated by modulator 112 with thesensed signal received at input 102. In this way, variable gainamplifier 114 is configured to operate as an analog mixer, and attenuatethe off-band noise components (those that are outside of the sensingchannel passband) of a sensing channel, as discussed above. Additionaldetails of configurations of variable gain amplifiers are discussed ingreater detail below with reference to FIGS. 3A-3C.

FIG. 2 illustrates an example of a system for enhancing noise immunityof capacitive sensors, configured in accordance with some embodiments.As similarly discussed above, a capacitive sensor may include variouscomponents configured to utilize capacitance measurements to identifythe presence of objects. For example, a capacitive sensor may utilizevarious electrodes to sense the presence or contact with a user's fingerbased on capacitance-based measurements. In various embodiments, asystem, such as system 200, may be configured to initialize and utilizea signal generator to reduce noise, and therefore improve theSignal-to-Noise ratio.

Accordingly, system 200 includes attenuator 202 which is configured toset an input impedance seen by a sensing device, such as a touch panel,and also configured to set an output impedance seen by other componentsof system 200 discussed in greater detail below. Accordingly, attenuator202 may be configured to decrease an input current and provide a lowinput impedance for a touch panel input current. Moreover, attenuator202 may be further configured to provide a high output impedance forvarious components, such as capacitors discussed in greater detailbelow. In various embodiments, attenuator 202 as well as components ofsystem 200 are implemented as a sensing channel of a capacitive sensor.In various embodiments, the sensing channel operates as a chargebalancing charge-to-the-time converter circuit.

System 200 also includes signal generator 204 which is configured togenerate a gain control signal that is provided to attenuator 202, andconfigured to reduce particular characteristics of an input signalsensed at an input, which may be received from one or more electrodes ina touch panel. As will be discussed in greater detail below, in someembodiments, signal generator 204 is configured to include a demodulatorthat is configured to generate a rectified sinusoidal waveform that maybe provided to attenuator 202. Accordingly, an output signal generatedby signal generator 204 may be used to change the gain of attenuator 202in accordance with the output signal. When configured in this way,attenuator 202 operates as an analog mixer that multiplies the inputsignal received from sensing electrodes with the rectified sinusoidalwaveform. Therefore, a gain of attenuator 202 changes in, for example, arange 0 . . . K_(MAX), where the K_(MAX) is maximum level of the gain.In various embodiments, an attenuator input signal is bipolar, but thegain change factor is unipolar. In some embodiments, signal generator204 is configured to implement a look-up-table (LUT) that is used todetermine values of the gain of signal generator 204 usingpre-programmed set of gain levels. Accordingly, a pre-programmed LUT maybe used instead of a demodulator. Moreover, as will also be discussed ingreater detail below, signal generator 204 may be further configured toimplement windowing via a window function to further narrow a frequencyresponse peak, and to further increase the noise attenuation of system200 and improvement of the Signal-to-Noise ratio. In variousembodiments, signal generator 204 is implemented using single-bit (duallevel) or multi-bit (multi-level) sigma-delta modulators.

System 200 further includes first integration capacitor 206 and secondintegration capacitor 208 which are configured to implement variousoperations, such as balancing of an output of the integrated chargecoming from attenuator 202 that may be generated based on a received orsensed input. Accordingly, first integration capacitor 206 may be aneven phase integration capacitor, and second integration capacitor maybe an odd phase integration capacitor, and together they may implementtime-separated (interlaced) phases of charge accumulation and balancing.In various embodiments, an output of system 200 is generated usingbalancing time intervals that are represented as numerical valuesdetermined in proportion to the total charge integrated by one or moreof the integration capacitors during half of a transmit period or otherappropriate time interval. The integration of multiple balancingintervals (e.g. for 10 transmit periods, and 20 intervals in total)produces a baseline value.

System 200 additionally includes current source 210, which may be abalancing current source, configured to generate a current associatedwith first integration capacitor 206 and second integration capacitor208 discussed above. In various embodiments, the current is used tocharge first integration capacitor 206 and second integration capacitor208. For example, a digitizer may use the current to charge anddischarge the integration capacitors. Thus, current source 210 may haveseveral different uses, depending on particular features of the sensingchannel in which it is included. In one example, it might be used forboth digitization and calibration associated with balancing operations.Accordingly, current source 210 may include source and sink currentsources that are configured to generate the appropriate current usedduring balancing operations. As shown in FIG. 2, current source 210,first integration capacitor 206, and second integration capacitor 208may be coupled to comparator 212, which may be configured to detectchanges of voltages of first integration capacitor 206 and secondintegration capacitor 208 with respect to a reference voltage.

System 200 further includes controller 214 configured to measure anoutput of comparator 212, as well as generate various different controlsignals used by other components of system 200. For example, controller214 may be configured to generate control signals for balancingoperations, for control over coupling of first integration capacitor 206and second integration capacitor 208, a reset operation, as well asinitialization of attenuator 202 at the beginning of a capacitanceconversion. In this way, controller 214 may obtain measurements made bythe sensing channel implemented by system 200, and may control variouscomponents within system 200.

FIG. 3A illustrates an example of an attenuator, configured inaccordance with some embodiments. As discussed above, an attenuator,such as attenuator 302, may be implemented in the context of a sensingchannel, and may have its gain modulated to reduce or attenuateundesirable noise characteristics of a sensed signal, as may occur atodd harmonics of a scanning frequency. Accordingly, attenuator 302 maybe specifically configured to implement a variable gain in such amanner.

More specifically, attenuator 302 may include input stage 304, which mayhave a fixed gain, and output stage 306, which may have a variable gain.As shown in FIG. 3A, input stage 304 includes operational amplifier 308,and output stage 306 includes multiple current mirrors, such as currentmirror 310. Moreover, output stage 306 includes multiple switches, suchas set of switches 312, such that each current mirror has an individualswitch, and each current mirror may be selectively coupled or decoupledto the output of attenuator 302. In various embodiments, the switchesare controlled via control signals to dynamically couple and decouplevarious current mirrors during a sensing operation. In this way,operation of the switches may be controlled to implement current summingof the current mirrors in a dynamically configurable manner where anamplitude of the output current of attenuator 302 is directlyproportional to the number of coupled current mirrors. As discussedabove, such control signals may be generated by a component, such as acontroller.

As also discussed above, the output of attenuator 302 may be coupled toone or more capacitors, such as integration capacitors (Cint).Accordingly, configuration of the gain of attenuator 302 may affect theoutput current so the attenuator gain modulation affects a total chargein an integration capacitor and a corresponding voltage on theintegration capacitor. Due to the configuration of the implementation ofmultiplication of the input signal on the rectified sinusoidal signal,off-band noise is attenuated, so sensitivity to odd harmonics of thetransmit frequency is reduced.

FIG. 3B illustrates another example of an attenuator, configured inaccordance with some embodiments. As discussed above, an attenuator,such as attenuator 320, may be implemented in the context of a sensingchannel, and may have its gain modulated to reduce or attenuateundesirable noise characteristics of a sensed signal, as may occur atodd harmonics of a scanning frequency. As also discussed above,attenuator 320 may include input stage 322 and output stage 324 whichmay include various current mirrors and switches.

As discussed above with reference to FIG. 3A, switches may be used tocontrol current mirror outputs for currents summing. As shown in FIG.3B, switches, such as switch 326, may be used to control gate circuitsof the current mirrors. Accordingly, as shown in FIG. 3B, theconfiguration of the current mirrors and switches may be implementedsuch that gate switching is used to control operation of the currentmirrors. Accordingly, control signals may be generated to dynamicallycontrol operation of gate switches as well as activation of transistorsincluded in the current mirrors. Thus, in various embodiments, gateswitches may be used to modify an output current of attenuator 320 aswell as a voltage applied to downstream integration capacitors.

FIG. 3C illustrates yet another example of a variable gain attenuator,configured in accordance with some embodiments. As discussed above, anattenuator, such as attenuator 330, may be implemented in the context ofa sensing channel, and may have its gain modulated to reduce orattenuate undesirable noise characteristics of a sensed signal, as mayoccur at odd harmonics of a scanning frequency. In various embodiments,attenuator 330 is configured to use low-voltage, low-injectiondifferential stages to implement current switching between integrationcapacitors and an analog buffer. In various embodiments, thedifferential current switches re-distribute current mirror outputcurrent between an integration capacitor and a buffer output.Distributing current in this way ensures that a voltage on theintegration capacitor remains the same, and provides the ultra-lowinjection gain adjustment.

Accordingly, attenuator 330 may include stage 332 and stage 334 whichmay be coupled to integration capacitor 336 and buffer 338. As shown inFIG. 3C, stage 332 may be a differential stage that operates at arelatively lower switching voltage, such as 100 mV. Accordingly, theconfiguration of stage 332 results in a lower parasitic injection inintegration capacitor 336. Moreover, stage 334 may include componentssimilar to those shown in stage 332 In various embodiments, attenuator330 may include one or more differential current switch stages, such asstage 332. In various embodiments, an output current going tointegration capacitor 340 is determined by a number of the stages thatare active or “turned-on” at same time, and this number varies based ona half-period of a rectified sinusoidal waveform, as similarly discussedabove.

Moreover, while FIG. 3C illustrates attenuator 330 has having twoidentical differential current switches, it will be appreciated thatattenuator 330 may have any number of differential current switches. Forexample, a number of current switches may be determined based on one ormore features of an output of a modulator, as discussed above. Morespecifically, the modulator may be a multi-level delta-sigma modulator,and the number of stages may be determined based on the number of levelsused by the delta-sigma modulator.

FIG. 4 illustrates another example of a system for noise immunityenhancement of capacitive sensors, configured in accordance with someembodiments. As similarly discussed above, a system, such as system 400,may be configured to initialize and utilize a signal generator to reducenoise and increase the signal to-noise ratio when making measurements.As also discussed above, system 400 may include attenuator 402, firstintegration capacitor 406, second integration capacitor 408, currentsource 410, comparator 412, and controller 414.

As shown in FIG. 4, system 400 additionally includes switch 416 which isincluded in attenuator feedback path 418. When turned-on, switch 416couples a current output of attenuator 402 back to its sensed input, andattenuator 402 is set in a reset or initialized state. Morespecifically, switch 416 may be turned-on to keep attenuator 402 in thereset state when the integration capacitors are disconnected, thuspreventing parasitic charge accumulation at the attenuator output stage.In various embodiments, control signals may be specifically configuredto control the operation of switch 416 as well as other components toreduce parasitic charge accumulation and thus reduce the noise presentin obtained measurements. More specifically, a control signal may beconfigured to control the operation of switch 416, and additionalcontrol signals may be configured to control the operation of switches420 and switches 422 coupled to first integration capacitor 406 andsecond integration capacitor 408. The control signals may be generatedbased on values stored in a timer table, and thus may be generated basedon a table of data values that operates as a LUT. Such a timer table maybe stored in a set of registers, and may include data values that definesequences of coupling and uncoupling of switches in a manner that may beimplemented periodically.

As will be discussed in greater detail below, the timer table may begenerated by first implementing a frequency sweep to identifyfrequencies that need to be attenuated, and then generating the timertable based on the identified frequencies. In this way, values of thecontrol signals and operation of the switches may be implemented using aLUT during scanning operations. Accordingly, a switch control signal maybe a single-bit representation of a rectified sinusoidal signal and canbe generated in any suitable way (e.g. via implementation of asingle-bit sigma-delta modulator, LUT, timer-table etc.).

FIG. 5A illustrates an implementation of an attenuator, configured inaccordance with some embodiments. As also discussed above, anattenuator, such as attenuator 502, may be configured such that an inputto the attenuator is modulated to reduce sensitivity to off-bandtransmit frequency components. As shown in FIG. 5A, attenuator 502 maybe coupled to input controller 504 that includes switch 506. In variousembodiments, switch 506 is configured to toggle coupling between asensed input and different inputs of attenuator 502. For example, in afirst position, switch 506 may couple the input to a first input ofattenuator 502, which is also coupled to a feedback path. In a secondposition, switch 506 couples the input to the second input of attenuator502, which is also coupled to a reference voltage. In variousembodiments, switch 506 may be a single-pole double throw (SPDT) switch.Moreover, operation of switch 506 may be controlled via a timer tableconfigured as a LUT, as discussed above. Therefore, switch 506 isconfigured to provide a single bit (dual level: gain factor is zero orone) discrete-time mixer that reduces external, out of transmit bandnoise components similar to other discrete time mixer/variable gainattenuator implementations as discussed above with reference to FIGS.3A-3C.

FIG. 5B illustrates an implementation of an attenuator, configured inaccordance with some embodiments. As similarly discussed above, anattenuator, such as attenuator 510, may be configured such that an inputto the attenuator is modulated. As also discussed above, attenuator 510may be coupled to input controller 512 that includes first switch 514and second switch 516. In various embodiments, first switch 514 isconfigured to selectively couple and decouple a sensed input from aglobal bus of the sensing channel associated with attenuator 510.Moreover, second switch 516 is configured to selectively couple anddecouple the sensed input to an input of attenuator 510. Furthermore,third switch 518 may be implemented to couple and decouple the globalbus from a reference voltage. As similarly discussed above, operation offirst switch 514 and second switch 516 are controlled via a timer tableconfigured as a LUT. In various embodiments, switches 514, 516, and 518might be part of a programmable touch panel multiplexer structure.

FIG. 6 illustrates an example of a system for noise immunity enhancementof capacitive sensors, configured in accordance with some embodiments.As similarly discussed above, a system, such as system 600, mayconfigure and utilize a signal generator to reduce noise and increasethe sensitivity of components used to make such measurements.Accordingly, system 600 may include attenuator 602, capacitor 604,resistor 606, and signal generator 608. In some embodiments, resistor606 and capacitor 604 may be representational of an equivalentresistance and capacitance provided by a touch panel in aself-capacitance sensing mode.

As shown in FIG. 6, system 600 additionally includes programmableattenuator 610, which may be a multi-gain level attenuator, and whichmay be programmable to select a gain applied to an input of attenuator602. For example, programmable attenuator 610 may include a multiplexer,such as multiplexer 612 that may be configured to select a particularinput coupling path provided between an input of multiplexer 612 andattenuator 602. Each different path may have a different gain, andselection of the path may be controlled by the signal provided by signalgenerator 608. Thus, selection of the path provided by multiplexer 612can be used to modify an input gain provided to attenuator 602 becauseeach different path has a different gain determined by a uniqueconfiguration of resistors. While operation of multiplexer 612 is shownas being controlled by signal generator 608, in some embodiments,operation of multiplexer 612 is controlled via a timer table configuredas a LUT. According to various embodiments, any suitable number of gainlevels may be used. For example, 8 gain levels might be supported in oneembodiment.

FIG. 7 illustrates an example of a system for noise immunity enhancementof capacitive sensors, configured in accordance with some embodiments.As discussed above, systems disclosed herein are configured to obtainimpedance and capacitance measurements, and identify hover and touchevents based on such measurements, as may occur when a user hovers ortouches a sensing device. Accordingly, a system, such as system 700 mayinclude such a sensing device as may be implemented in the context of acapacitive sensor.

Accordingly, system 700 includes sensing device 702 which may includecomponents, such as electrodes configured to sense changes in measuredelectrical properties within a designated distance of the sensingdevice. As discussed above, sensing device may be a touch screen, touchpanel, or button that includes one or more electrodes. In one example,the electrodes may be arranged in arrays of transmit and receiveelectrodes, where the transmit electrodes are configured to transmit asignal in accordance with a scanning protocol or sequence, and thereceive electrodes are configured to receive the signal, thus obtainingsensed measurements of an impedance between the two.

System 700 additionally includes one or more sensing channel 704 whichis configured to receive the signal sensed by sensing device 702, as maybe generated by receive electrodes included in sensing device. Asdiscussed above, sensing channel 704 includes various components, suchas an attenuator and integration capacitors. Additional detailsregarding the operation of sensing channel have been discussed above. Asshown in FIG. 7, sensing channel 704 may also be coupled to components,such as first signal generator 706 and processing unit 708. As discussedabove, first signal generator 706 may generate a signal that isconfigured to reduce noise that may be present in the measurementsobtained by sensing channel 704, and may be caused by various sourcessuch as parasitic capacitances. Furthermore, processing unit 708 may beconfigured to include a controller as discussed above, as well as one ormore processors configured to implement other sensing operations. Forexample, processing unit 708 may be configured to identify and storemeasurement data in a memory device, as well as perform one of morecomputations to identify particular events, such as hover events andtouch events. While first signal generator 706 and processing unit 708have been shown as coupled to sensing channel 704, it will beappreciated that first signal generator 706 and processing unit 708 maybe included in sensing channel 704.

System 700 further includes transmit channel 710 which is configured togenerate a signal provided to sensing device 702 that provides thesignal used during a scanning sequence, and forms the basis ofsubsequent measurements. Accordingly, transmit channel 710 may includevarious components such as an amplifier and/or a buffer as well as acurrent source and/or a voltage source. As shown in FIG. 7, transmitchannel 710 may be coupled to second signal generator 712 as well ascharge pump 714. Accordingly, second signal generator 712 may beconfigured to generate a signal used to drive transmit electrodes duringa scanning sequence, and thus may configure the parameters of such adrive signal. Charge pump 714 may be configured to voltage regulationfor transmit channel 710. Moreover, multiplexer 720 may be configured toselectively couple sensing channel 704 and transmit channel 710 withparticular electrodes of sensing device 702 in accordance with ascanning sequence. Accordingly, multiplexer 720 may include a transmitmultiplexer for transmit electrodes and a sensing multiplexer forsensing, also referred to herein as receive, electrodes.

FIG. 8 illustrates a flow chart of an example of a method forsensitivity enhancement of capacitive sensors, implemented in accordancewith some embodiments. As discussed above, a capacitive sensor mayinclude various components configured to utilize capacitancemeasurements to identify the presence of objects. For example, acapacitive sensor may utilize various electrodes to sense the presenceor contact with a user's finger based on capacitance-based measurements.As also discussed above, operation of an attenuator gain may bemodulated to reduce noise and increase the signal to noise ratio formeasurements when sensing operations are performed by the capacitivesensor. Thus, according to various embodiments, a method, such as method800, may be implemented during run time to reduce noise that maymanifest at odd harmonics.

Accordingly, method 800 may commence with operation 802 during which atransmit signal generator and a sensing signal generator may beinitialized based, at least in part, on a plurality of demodulationparameters. As discussed above, the transmit signal generator may beincluded in a transmit channel and used to drive transmit electrodesduring a scanning sequence. Thus, during operation 802, the transmitsignal generator may be initialized based on a designated scanningsequence or protocol. Moreover, a sensing signal generator may be asignal generator implemented in the sensing channel and used to modulateoperation of one or more components of the sensing channel, as discussedabove. For example, the signal generator may modulate a gain of theattenuator included in the sensing channel. Accordingly, duringoperation 802, the sensing signal generator may be initialized.

Method 800 may proceed to operation 804 during which a scan of aplurality of electrodes of a capacitive sensing device may beimplemented. Accordingly, a scanning sequence may be implemented. Aswill be discussed in greater detail below, the scanning sequence may beimplemented in accordance with designated scanning parameters, andmeasurements may be made based on sensed inputs received from thesensing device, and in accordance with the operation of the sensingsignal generator, as similarly discussed above.

Method 800 may proceed to operation 806 during which scanning data maybe collected based, at least in part, on the scan of the plurality ofelectrodes. Accordingly, the measured data may be stored in a memorydevice. Moreover, one or more computations may be implemented. Forexample, the measurements may be used to identify one or more events,such as touch events and/or hover events. Such computations may be madebased on comparisons of the measurements to one or more thresholdvalues, or any suitable event detection technique.

FIG. 9 illustrates a flow chart of another example of a method forsensitivity enhancement of capacitive sensors, implemented in accordancewith some embodiments. As discussed above, a unique configuration ofsignal generators in a capacitive sensor may be implemented during runtime to reduce noise in measurements that may manifest at, for example,odd harmonics. Accordingly, a method, such as method 900 may beimplemented to control the operation of such signal generators andenhance the sensitivity of capacitive sensors, as discussed above.

Method 900 may commence with operation 902 during which one or morecapacitive sensor electrodes may be initialized. In various embodiments,components such as signal generators and current sources may beinitialized and configured based on one or more configurationparameters. In some embodiments of capacitance sensing configurations, anumber of touch panel receive electrodes is much greater than a numberof sensing channels. Accordingly, the entire panel needs to be scannedin several scanning slots, where in a particular scanning slot, aparticular sensing channel connects a selected set of several electrodesin series during a particular scanning slot. Accordingly, as usedherein, a scanning slot may be a particular configuration or set of asensing channel and sensing electrodes that may be selected duringseveral iterations of scanning used to scan an entire capacitive sensorwhich may include a touch panel.

Method 900 may proceed to operation 904 during which one or moremultiplexers may be configured based on a designated scanning position.As discussed above, sensing devices may include multiple transmit andsensing electrodes that may be arranged in arrays having intersectionpoints. In various embodiments, the electrodes may be scannedsequentially. Accordingly, during operation 904, a transmit and sensingmultiplexer may be configured to select a particular electrode from thetransmit electrodes and sensing electrodes. In various embodiments, suchelectrodes may be indexed by an identifier stored and maintained by acontroller, and the multiplexers may be set based on a received selectsignal.

Method 900 may proceed to operation 906 during which the transmit signalgenerator and the sensing signal generator may be initializedsynchronously. Accordingly, the transmit signal generator may beinitialized and started, and the sensing signal generator may beinitialized and started at the same time. As discussed above, thesequences and output of the signal generators are configured such thatthe transmit signal generator generates a drive signal used to drivetransmit electrodes in sensing device, and the sensing signal generatorgenerates a signal that modulates one or more components of the sensingchannel to reduce and mitigate noise components of the sensed signalreceived in response to the drive signal. For example, the sensingsignal generator may periodically modulate the gain of the attenuator ofthe sensing channel to effectively remove a noise component of thesensed signal.

Method 900 may proceed to operation 908 during which a scanning sequencemay be implemented. Accordingly, as discussed above, once the signalgenerators have been initialized, the scanning sequence may beimplemented for the selected electrode pair. The scanning sequence maybe implemented at a particular scanning frequency and amplitude. Thus,during operation 908, the transmit signal generator may drive thetransmit electrodes at a scanning frequency in accordance with scanningparameters, and the sensing signal generator generates a signal used toreduce noise components of the signal sensed in response to the drivesignal. As previously discussed, this may include modulating the gain ofan attenuator, and/or operating one or more switches implemented incombination with the attenuator.

Method 900 may proceed to operation 910 during which scanning data maybe collected based, at least in part, on the scanning sequence. Asdiscussed above, measurements may be made at a designated sampling rate,and the measured data may be stored in a memory device. As alsodiscussed above, one or more computations may be implemented. Forexample, the measurements may be used to identify one or more events,such as touch events and/or hover events. Such computations may be madebased on comparisons of the measurements to one or more thresholdvalues, or any suitable event detection technique. In some embodiments,such computations may be made after all measurement data has beenacquired from all electrodes.

Method 900 may proceed to operation 912 during which. It may bedetermined if additional scanning should be implemented. In variousembodiments, such a determination may be made based on one or moreaspects of the sensing device. As discussed above, the sensing devicemay include multiple electrodes that may be identified based on an indexor an identifier. During a scanning sequence, the electrodes may bescanned sequentially. Accordingly, a controller may cycle through theelectrodes until the last electrode is scanned, as may be determinedbased on the identifier. In one example, the controller may use a statemachine configured to cycle through the electrodes in this manner. Thus,if it is determined that additional scanning should be implemented,method 900 may return to operation 904, and a different set ofelectrodes may be selected and scanned. If it is determined that noadditional scanning should be implemented, method 900 may terminate.

FIG. 10 illustrates a flow chart of an additional example of a methodfor sensitivity enhancement of capacitive sensors based on transmitsignal phase adjustments, implemented in accordance with someembodiments. As discussed above, a unique configuration of signalgenerators in a capacitive sensor may be implemented during run time toreduce noise in measurements that may manifest at, for example, oddharmonics. Furthermore, a method, such as method 1000 may be implementedto calibrate a transmit signal generator to compensate for phase shiftsintroduced by components of a capacitive sensor, and thus increase theefficacy of the combination of signal generators discussed above. Invarious embodiments, to further increase sensitivity of capacitivesensors, an input sinusoidal waveform is phase aligned with anattenuator gain control signal. This alignment is accomplished based ona phase calibration procedure, discussed in greater detail below.

Method 1000 may commence with operation 1002 during which one or moremultiplexers may be configured based on a designated scanning position.As discussed above, sensing devices may include multiple transmit andsensing electrodes that may be scanned sequentially. Accordingly, duringoperation 1002, a transmit and sensing multiplexer may be configured toselect a particular electrode from the transmit electrodes and sensingelectrodes. In various embodiments, such electrodes may be indexed by anidentifier stored and maintained by a controller, and the multiplexersmay be set based on a received select signal.

Method 1000 may proceed to operation 1004 during which a sensing signalgenerator and a transmit signal generator may be initialized. Asdiscussed above, components such as signal generators and currentsources may be initialized and configured based on one or moreconfiguration parameters. Accordingly, during operation 1004, a sensingsignal generator may be aligned in phase with a current source for thatchannel. Similarly, phase alignment may be implemented for components ofthe transmit channel.

Method 1000 may proceed to operation 1006 during which an initial phaseoffset value may be identified and retrieved. In various embodiments, aphase offset value may be identified for the transmit signal generator.Such a phase offset value may have been stored as a designated defaultphase value to be used at the beginning of a calibration procedure. Sucha value may have been determined by a manufacturer or user during aninitial configuration of the capacitive sensor. In one example, theinitial phase offset value may be a value of 0, and the phase offsetvalue may be increased in designated increments, as will be discussed ingreater detail below.

Method 1000 may proceed to operation 1008 during which the transmitsignal generator may be initialized based on the phase offset value.Accordingly, the transmit signal generator may be configured toimplement the phase offset when generating an output signal. In thisway, the phase offset may be implemented with driving the transmitelectrodes of the capacitive sensing device.

Method 1000 may proceed to operation 1010 during which a scanningsequence may be implemented. Accordingly, as discussed above, once thesignal generators have been initialized and the phase offset value hasbeen loaded, the scanning sequence may be implemented. The scanningsequence may be implemented at a particular scanning frequency andamplitude. Thus, during operation 1010, the transmit signal generatormay drive the transmit electrodes at a scanning frequency in accordancewith scanning parameters, and the sensing signal generator generates asignal used to reduce noise components of the signal sensed in responseto the drive signal.

Method 1000 may proceed to operation 1012 during which a baseline valuemay be calculated and stored for the phase offset value. Accordingly,the measurement data may be stored, and a baseline value may be computedthat represents a baseline amplitude or magnitude of the receivedsignal. Accordingly, one or more averaging techniques or othercomputational techniques may be implemented to compute a baseline valuerepresentative of a sensitivity of the sensing channel at the selectedphase offset value. In various embodiments, the baseline value can beproportional to the total output of the charge to time converter, asdiscussed above, with reference to FIG. 2 and FIG. 4. For example, thebaseline value may be computed by summing the balancing time intervalsfor a scanning burst (for example, for 10 transmit periods).

Method 1000 may proceed to operation 1014 during which it may bedetermined if a maximum phase offset has been reached. In variousembodiments, such a determination may be made by a controller based, atleast in part, on the phase offset value itself. As previouslydiscussed, the phase offset value may be set at an initial value, andmay be incremented through a designated range. Accordingly, thecontroller may include a state machine configured to step through theoffset value increments until a maximum value is reached. In someembodiments, the maximum value may be a designated value set by a useror manufacturer. For example, the maximum value may correspond to aphase offset of a full period or a half period of the transmit frequencyused by the transmit signal generator. If it has been determined that amaximum phase offset value has not been reached, method 1000 may proceedto operation 1016.

Method 1000 may proceed to operation 1016 during which the phase offsetvalue may be incremented. As discussed above, the phase offset value maybe incremented in accordance with a designated incrementation scheme.More specifically, the controller may be configured to increment thephase offset value by a designated amount, such as a designated numberof degrees, and the incremented value may be stored as the new phaseoffset value to be used. Method 1000 may then return to operation 1008and additional measurements may be made, and additional baseline valuesmay be computed until the maximum phase offset value has been reached.

Returning to operation 1014, if it has been determined that the maximumphase offset value has been reached, method 1000 may proceed tooperation 1018 during which a peak baseline value may be identified.Accordingly, the computed baseline values may be compared, and a maximumbaseline value may be identified that has a highest baseline value. Thephase offset value associated with the maximum baseline value may alsobe identified.

Method 1000 may proceed to operation 1020 during which the phase offsetvalue associated with the peak baseline value may be selected and storedas a phase offset value for the transmit signal generator. Accordingly,the phase offset value identified during operation 1018 may be stored ina memory device, and may be used to initialize and configure thetransmit signal generator during subsequent scanning operations. In thisway, the transmit signal generator may be configured to compensate forvarious phase shifts introduced by components included in a capacitivesensor.

FIGS. 11A and 11B illustrate diagrams of examples of an attenuator inputand output having different numbers of gain steps, implemented inaccordance with some embodiments. More specifically, FIG. 11Aillustrates attenuator input current 1102 and attenuator output current1104 for an attenuator having seven gain levels implemented with a 3-bitquantizer. Moreover, FIG. 11B illustrates attenuator input current 1106and attenuator output current 1108 for an attenuator having two gainlevels implemented with a 1-bit quantizer. In various embodiments, theoutput currents approximate a sin²(t) function similar to a traditionalanalog multiplier. As shown in FIGS. 11A and 11B, an increase in anumber of gain levels may provide better approximation of the sinusoidalsignal.

FIGS. 12A and 12B illustrate diagrams of examples of signals sensed byone or more sensing channels, implemented in accordance with someembodiments. More specifically, FIG. 12A illustrates a sensed signal ata particular transmit frequency, where the sensed signal is sensed by asensing channel that is not configured to provide noise immunity, asdisclosed herein. In various embodiments, the sensing of the transmitsignal at the transmit frequency, also referred to herein as anoperation frequency, is represented by peak 1202. FIG. 12A furtherillustrates additional peaks at odd harmonics of the operationfrequency, such as peak 1204, peak 1206, peak 1208, and peak 1210. Asdiscussed above, such peaks are measurement noise that degrade theoverall signal-to-noise ration of the capacitive sensor.

In various embodiments, FIG. 12B illustrates a sensed signal at aparticular transmit frequency, where the sensed signal is sensed by asensing channel that is configured to provide noise immunity, asdisclosed herein. Accordingly, the sensing of the transmit signal at thetransmit frequency is represented by peak 1212. As shown in FIG. 12B,there are no other peaks associated with odd harmonics. Accordingly, thepeaks in the measured signal caused by the odd harmonics has beenremoved, and the overall signal-to-noise ratio of the capacitive sensorhas been improved.

Although the foregoing concepts have been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. It should be noted that there are many alternative waysof implementing the processes, systems, and devices. Accordingly, thepresent examples are to be considered as illustrative and notrestrictive.

What is claimed is:
 1. A device comprising: an attenuator configured toreceive an input from at least one sense electrode of a capacitivesensing device, the attenuator being included in a sensing channel of acapacitive sensor; and a signal generator coupled to an input of theattenuator, the signal generator comprising one or more processorsconfigured to: generate a sinusoidal signal based, at least in part, onone or more noise characteristics of a scan sequence associated with oneor more transmit electrodes of the capacitive sensing device; andprovide the sinusoidal signal to the input of the attenuator.
 2. Thedevice of claim 1, wherein the signal generator comprises a sinusoidalmodulator.
 3. The device of claim 2, wherein the device furthercomprises: a mixer configured to combine the sinusoidal signal receivedfrom the signal generator and the input received from the at least onesense electrode, and further configured to generate an output based onthe combining.
 4. The device of claim 3, wherein the mixer is a variablegain amplifier configured to change gain based on a gain control signal.5. The device of claim 1, wherein the signal generator is configured touse the sinusoidal signal to modulate a gain of the attenuator, andwherein the sinusoidal signal is a rectified sinusoidal signal.
 6. Thedevice of claim 1, wherein the signal generator is configured to providethe sinusoidal signal to the attenuator during the scan sequence.
 7. Thedevice of claim 1, wherein the signal generator is further configured toimplement a window function.
 8. The device of claim 1, wherein the atleast one sense electrode and the one or more transmit electrodes areincluded in an electrode array of a capacitive touch screen.
 9. Thedevice of claim 1, wherein the signal generator is configured to besynchronous with a transmit signal generator, and wherein the transmitsignal generator is configured to implement a phase offset value. 10.The device of claim 9, wherein the phase offset is determined based on apeak response of the capacitive sensor.
 11. A method comprising:generating a transmit drive signal based, at least in part, on one ormore scanning parameters, the transmit drive signal being provided toone or more transmit electrodes of a capacitive sensing device;generating, using a signal generator, a sinusoidal signal based, atleast in part, on one or more noise characteristics of the transmitdrive signal and capacitive sensing device; receiving a sensed signalfrom at least one sense electrode of the capacitive sensing device; andreducing the one or more noise characteristics in the sensed signalbased, at least in part, on the sinusoidal signal.
 12. The method ofclaim 11, wherein the signal generator comprises a sinusoidal modulator.13. The method of claim 11, wherein the reducing comprises: combining,using a mixer, the sensed signal with the sinusoidal signal at an inputof an attenuator.
 14. The method of claim 13, wherein the mixer is avariable gain amplifier configured to change gain based on a gaincontrol signal.
 15. The method of claim 11, wherein the reducingcomprises: modulating a gain of an attenuator based, at least in part,on the sinusoidal signal.
 16. A system comprising: a plurality of senseelectrodes implemented in a capacitive sensing device; a plurality oftransmit electrodes implemented in the capacitive sensing device; and anattenuator configured to receive an input from at least one of theplurality of sense electrodes, the attenuator being included in asensing channel of a capacitive sensor; and a signal generator coupledto an input of the attenuator, the signal generator comprising one ormore processors configured to: generate a sinusoidal signal based, atleast in part, on one or more noise characteristics of a scan sequenceassociated with one or more transmit electrodes of the capacitivesensing device; provide the sinusoidal signal to the input of theattenuator; and a controller configured to implement the scan sequenceand obtain a plurality of measurements based on the scan sequence. 17.The system of claim 16, wherein the signal generator comprises asinusoidal modulator.
 18. The system of claim 17, wherein the devicefurther comprises: a mixer configured to combine the sinusoidal signalreceived from the signal generator and the input received from the atleast one of the plurality of sense electrodes, and further configuredto generate an output based on the combining.
 19. The system of claim16, wherein the signal generator is configured to use the sinusoidalsignal to modulate a gain of the attenuator.
 20. The system of claim 16,wherein the signal generator is configured to provide the sinusoidalsignal to the attenuator during the scan sequence.